A multiple-cutting edge drill with a sharp drill point is disclosed in a Chinese patent No. ZL200820165519.5, which has a better centering ability than that of an ordinary multi-facet drill. In addition, by using the multiple-cutting edge drill, a less axial resistance can be achieved.
However, the multiple-cutting edge drill also has the following disadvantages.
In theory, an included angle between two inner cutting edges of the multiple-cutting edge drill can be controlled and does not increase excessively. However, in operation, the included angle between two inner cutting edges ranges from about 124° to about 133°, which means there is still a certain increment of the angle included between the two inner cutting edges, so that promotion of the centering ability of the multiple-cutting edge drill is limited to a certain degree. Moreover, when the multiple-cutting edge drill is used, the axial resistance does not increase excessively, but it still increases to some extent.
A length of a dill point of the multiple-cutting edge drill is less than that of a twist drill so that a drilling process performed to thin-wall materials by using the multiple-cutting edge drill is ended before a countersink with an enough size for centering is formed, which induces a poor stability and bad roundness of holes while drilling sheets or circular pipes.
Although a good performance can be achieved when the multiple-cutting edge drill with the included angle between inner cutting edges ranging from about 124° to about 133° is used to drill holes in hard materials such as drill steel, cast iron, and stainless steel, but a deviation and the bad roundness of holes may be induced when the multiple-cutting edge drill is used to drill holes in materials such as aluminum, wood, and plastic, because the drill point of the multiple-cutting edge drill is not sharp enough so that a guidance capability is poor.